cascading python executions only if return code is 0

Ethan Furman ethan at
Mon Dec 23 13:45:07 CET 2013

On 12/22/2013 08:57 PM, Roy Smith wrote:
> In article <52b7a0e4$0$29994$c3e8da3$5496439d at>,
>   Steven D'Aprano <steve+comp.lang.python at> wrote:
>> Anyway, I may be completely misinterpreting what I'm reading. Perhaps the
>> assertion is checking a function invariant ("one of the strategies will
>> always succeed") in which case you're doing it exactly right and I should
>> shut up now :-)
> Yes :-)
> More specifically, the assertion exception will get caught way up in
> some django middleware which will log a stack trace and return a HTTP
> 50-something.  This will typically be followed by somebody like me
> noticing the stack dump and trying to figure out WTF happened.

This is completely misusing what assertions are for.  I hope this bit of middleware (or django itself) is very clear 
about never running with assertions turned off.

> Assertions are great tools.

Only when used properly.

>People should use them more often.

I see them being (mis)used too much as it is.

>In a
> sense, they're executable comments.  They're a programmer's way of
> standing on a hilltop and shouting to all the world, "I swear to you,
> this is true.  There may be a gazillion lines of code out there and
> GBytes of program state, but right here, right now, within this circle
> I've drawn in the sand,

Considering how easy it is to disable assertions, a circle in the sand is an amazingly appropriate metaphor.  :)


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